1. Field of the Invention
This invention relates to an ice forming apparatus and more particularly to such apparatus used for forming a solid ice layer on a relatively wide area such as a skating rink.
2. Prior Art
Formerly, in forming and maintaining a solid ice layer in the skating rink, the conventional practice is to lay a large number of freezing pipes consisting of bare steel pipes or synthetic resin pipes on a given site such as rink floor, and a liquefied gas such as freon or ammonia or an antifreeze liquid such as brine or ethylene glycol is circulated as freezing medium or refrigerant through the pipes for forming and maintaining the ice layer. A large number of such freezing pipes are each connected at one end to a refrigerant supply header and at the other end to a refrigerant return or outlet header. These headers are further connected to a freezing unit by way of feed and return pipes for circulating the refrigerant from the freezing pipe through the feed pipe, supply header, freezing pipe, outlet header and outlet pipe in this order and back to the freezing unit to complete a freezing cycle.
When freezing pipes are laid widthwise of the skating rink, the number of the freezing pipes may inevitably be increased, and the pipe installation operation is also complicated with additional costs. Hence, it is more customary that the freezing pipes be laid along the longitudinal direction of the rink in consideration of conveniences in the pipe installation operation, and cost efficiency.
Formerly, bare steel pipes have been used as freezing pipes. In recent times, however, resilient synthetic resin such as ethylene vinyl acetate (EVA) is preferred to steel as a freezing pipe material. The synthetic resin pipes are less costly and lightweight as compared with the steel pipes and may be made available in considerably long size, which facilitates transport, mounting and dismounting operations. Thus, the synthetic resin pipes may be advantageously employed with a multi-purpose sporting site serving both as a swimming pool during summer and as a skating rink during winter.
However, the synthetic resin pipe is not so durable as to be suited for long-term use and can hardly be used for a permanent rink or a skating rink made of reinforced concrete and having the freezing pipes permanently embedded in the concrete flooring, whereas the steel pipe is more durable and can be applied to such permanent rink.
One of the freezing systems for the skating rink is an indirect system in which an anti-freezing liquid, such as brine, is chilled in a freezing equipment comprising a heat exchanger to be circulated through the freezing pipe laid on a rink floor for freezing the water in the rink. Another freezing system is a direct system in which freon gas or ammonia is circulated directly through the freezing pipe and undergoes an expansion process for chilling the water. In case of the indirect freezing system, the freezing pipe is required to be large in diameter and wall thickness because of necessity for having the large amount of the anti-freezing liquid circulated in the freezing pipe. Thus, steel pipes are predominantly used in the indirect system, because it is technically difficult or unfeasible to use the synthetic resin pipe as freezing pipe for the indirect system.
As such steel pipes, naked pipes were used hithertofore as freezing pipes. This gives rise to the following inconveniences.
(1) The pipes in large lengths are usually kept from being used because of inconveniences in transport and installation operations as well as costs. Therefore, the pipes of shorter lengths such as those with lengths less than 5.50 meter are normally used so as to be necessarily welded at the construction site, causing additional labor and operational costs.
(2) In welding the pipe segments together, the welds are inevitably of a larger wall thickness and are liable to change in quality. Consequently, the welds exhibit a freezing effect different from that of the other pipe portions, and thus it is impossible to obtain an ice layer of uniform and homogeneous quality.
(3) The freezing medium may leak through the defective welds, in case of inadequate welding.
(4) Corrosion or pinholes may be generated in case of prolonged use. For avoiding the corrosion or pinholes, the pipe must have a sufficient wall thickness, which in turn gives rise to additional costs in material and increased difficulties in transport.
(5) In some countries, the use of freon or a similar liquefied gas is subject to government regulations. In Japan, for example, the following standards are set under the High Pressure Gas Regulation Act on the thickness of the pipe adapted for conveyance of the high pressure liquefied gas.
Wall thickness of pipe &gt;t+a with EQU t=(pD.degree.)/(200yz+0.8p)
where
t=minimum thickness of the pipe in mm PA1 p=design pressure in kg/cm.sup.2 PA1 D.degree.=outside diameter of pipe in mm PA1 y=allowance tensile stress of material in kg/mm PA1 z=efficiency of weld joint PA1 a=corrosion allowance of pipe
The standards are also set on the corrosion allowance a in such a way that a.gtoreq.1.00 mm for a bare steel pipe and a .gtoreq.0.5 mm for a steel pipe with a corrosion resistant painting. Under these government regulations, the bare steel pipe need be of a relatively large wall thickness as compared with the inside diameter of the pipe. For an example, when the bare steel pipe with the inside diameter of 12 mm is used in the usual manner as the freezing pipe, it is required that the minimum wall thickness be 0.67 mm or more and the corrosion allowance be 1.00 mm or more, the wall thickness of the pipe being then 1.67 mm or more.
(6) In case of the direct system, it is necessary that a steel pipe of a relatively small diameter be used as freezing pipe because of the pressure of the circulating medium such as freon or its cost. However, since the requirement in the above (5) must be satisfied, the wall thickness becomes too large with the result that the tube is not utilized economically.
(7) When the bare steel tube is used as freezing pipe, it may be chilled abruptly and the water surrounding the freezing pipe is frozen abruptly. Consequently, the lower portion of the ice layer surrounding the freezing tube is not sufficiently compatible with the upper portion of the ice layer and the ice tends to be cracked along the boundary zone.
(8) The ice temperature about the freezing pipe becomes too low and the ice temperature control is also difficult.
(9) While the air tends to adhere to the outer surface of the freezing steel pipe, since the freezing pipe is chilled abruptly as stated (7) above, the air tends to remain in the formed ice layer in a white bubble pattern.
(10) In forming the ice layer of the skating rink, the usual practice is to form a so-called base ice on which water is sprayed with a nozzle for forming an upper layer. In this case, the ice temperature of the base ice may become too low so that the sprayed water upon contacting with the base ice is frozen and there is not sufficient time for the air contained in the spray water to be discharged from the water, the air being thus entrapped in the ice as air bubbles in the upper ice layer and interfering with formation of the uniform ice.